Background: Lack of adherence to drug treatment is a major obstacle to disease control. Although many studies have examined adherence to antipsychotic treatment, they have generally suffered from lack of differentiation between persistence and compliance as 2 separate components of adherence.

Objectives: In an outpatient population, to (1) measure the proportion of atypical antipsychotic users who were still on antipsychotic treatment after 12 months, (2) measure the proportion of compliant users among them, and (3) identify the determinants of persistence and of compliance.

Method: We carried out a population-based cohort study using the Quebec Health Insurance Board database. Patients previously diagnosed with schizophrenia (ICD-9 criteria) and initiated on clozapine, olanzapine, quetiapine, or risperidone treatment between January 1, 1997, and August 31, 1999, were included. Patients still undergoing treatment with any atypical antipsychotic drug 1 year after their first prescription were considered persistent. Of these patients, those with a supply of drugs for at least 80% of the days were deemed compliant. To identify the characteristics associated with both outcomes, we built a multivariate logistic regression model using a stepwise procedure and calculated odds ratios and their 95% confidence interval.

Results: Of 6662 individuals initiated on treatment with atypical antipsychotics, 4495 (67.5%) were still on the treatment after 1 year, and 3534 (78.6% of those who persisted) were compliant. Patients more likely to be both persistent and compliant were those initiated on clozapine, those who received a treatment of medium or high intensity, those who had used atypical antipsychotics, those without a history of substance-use disorder, and those on welfare. On the other hand, patients who were prescribed their first atypical antipsychotic by a psychiatrist were more likely to be persistent, whereas those with a high comorbidity index and those aged 35 years or more were more likely to be compliant.

Conclusions: One year after treatment initiation, almost a third of patients were no longer treated with atypical antipsychotics. Of those still being treated, more than 20% were noncompliant. Further studies should focus on means of improving such erratic treatment behaviors.